Shortest Path Bridging (SPB) is an extension of Multiple Spanning Tree Protocol (MSTP), and shares link states in a network through Intermediate System to Intermediate System (ISIS) intra-domain routing information exchange protocol. Nodes in the network calculate the shortest path among the nodes at the same time. The SPB may be applied to a metro Ethernet or a data center Ethernet (also called Converged Enhanced Ethernet (CEE)). The SPB has the advantages of 802.1ah, and may be deployed in a metro network or a campus network.
SPB has two implementation modes: a Q-in-Q mode called a SPB-Virtual Local Area Network ID (SPBV), which is very complex and is not widely applied at the present, and a MAC-in-MAC mode called a Shortest Path Bridging MAC (SPBM), which is widely applied at the present.
Bridges configured with ISIS instances that have the same Area ID constitute a Domain, and bridges that have the same configuration abstract constitute a Region. One Domain includes one or more Regions. The boundary of Region is recognized automatically according to primary and secondary Multiple Spanning tree configuration Information Digests (MCIDs) contained in a Shortest Path Tree Bridge Protocol Data Unit (SPT BPDU) and an ISIS Hello Protocol Data Unit (IIH PDU) packets, and a mode for packet forwarding in the region is set by configuring a Virtual Local Area Network (VLAN) instance mapping relationship. The mode of packet forwarding may be Internal Spanning Tree (IST)/0, SPBM/4092, SPBV/4093, Traffic Engineer (TE)/4094, Multiple Spanning Tree Instance (MSTI)/Other.